1. Field of the Invention
The present invention relates to a susceptor used for a vapor phase epitaxial growth device for growing an epitaxial layer on a surface of a silicon wafer and, particularly, relates to a susceptor for a vapor phase epitaxial growth device capable of enabling a silicon wafer to be loaded on a fixed position on the susceptor as a result of preventing skidding when loading the wafer.
2. Description of the Related Art
A so-called single wafer vapor phase epitaxial growth device is known as a vapor phase epitaxial growth device for growing a high quality epitaxial film on a wafer surface.
In this kind of single wafer vapor phase epitaxial growth device, a disk-shaped susceptor formed by coating silicon carbide SiC on graphite as a mother material is provided in a channel-shaped chamber made by quartz, and a wafer is loaded on the susceptor and brought to react with various material gases passing through the chamber while heating the wafer by a heater arranged on an outer surface of the chamber, so as to grow an epitaxial film on the wafer.
On the surface of the susceptor for a wafer to be loaded, a recessed portion (depression) called a wafer pocket is formed, which is a little larger than the wafer and has a depth of about a wafer thickness, and a wafer is placed in this pocket.
There is a minute clearance for allowing reaction gases to path through between the wafer and the wafer pocket. Therefore, in a film forming process of an epitaxial film, a reaction film having the several dozen of nm order is deposited on an outer circumferential area on the back surface of the wafer; but a film thickness of this reaction film has to be as uniform as possible because it affects flatness of the wafer. Particularly, along with device design rules becoming finer, total control of thickness and shape considering even reaction films formed on the back surface of the wafer has become necessary.
However, when a growth reaction of an epitaxial film is performed in a state that the center of the wafer is deviated from the center of the wafer pocket, a clearance size between the wafer and the wafer pocket becomes uneven in the circumferential direction and, thereby, flatness of the wafer declines; that has been a disadvantage.
Given this factor, there is known a technique of preventing skidding of a wafer when loading the wafer on the susceptor by making a wafer loading surface of the susceptor a flat surface and forming through holes (having a diameter of 10 mm) allover the loading surface to release gases at the time of loading, wherein a ratio of opening areas is 5 to 10% (Patent Article 1).
However, it was found that, when dropping a wafer with super flatness on a susceptor having a high ratio of opening area of through holes or on a susceptor having large diameter holes, speed of releasing gases cannot be same between the through holes and the balance is lost, and that results in an opposite effect of causing skidding of wafers. A reason for this is considered that, when loading a wafer with high flatness on a wafer pocket manufactured with high accuracy, a minute clearance (a nanometer level) between the wafer and the wafer pocket becomes furthermore minuter and releasing of gases at the time of loading is attained only by the through holes. This wafer skidding problem appears notably particularly when dropping by a Bernoulli chuck a large diameter wafer with super flatness on a wafer pocket manufactured with high accuracy.
Patent Article 1: Japanese Unexamined Patent Publication No. H08-8198